Automatic rechargeable battery monitoring system

Abstract

An electronic device for monitoring the charge state of a rechargeable battery comprising a voltage sensor, a current sensor, a microprocessor, and a display. The voltage sensor is operatively connected to the microprocessor to provide to the microprocessor an electronic signal indicative of the voltage appearing across the terminals of the battery. The current sensor is operatively connected to the microprocessor to provide to the microprocessor an electronic signal indicative of the current between the terminals of the battery. Based on the signals received from the voltage and current sensors, the microprocessor calculates the total current discharge capacity of the battery and the present level of charge contained within the battery, and delivers electronic signals indicative of the total current discharge capacity and the present level of charge contained within the battery to the display means.

What is claimed is: 
     
       1. A method for monitoring and indicating the charge state of a rechargeable battery, said method comprising the steps of: sampling current into and out of said battery at repeated intervals,   sampling a voltage across a pair of terminals of said battery to sense when said voltage reaches a predetermined level,   integrating the sampled current from a charge value to a discharge value,   repeating the steps of current sampling and current integration, and calculating a present level of battery charge from either a full charged state to a present charge state or a fully discharged state to said present state,   calculating a total discharge capacity of said battery based on said integration each time said battery reaches said fully discharged state, such that said total discharge capacity comprises an approximation of a true total discharge capacity of said battery,   comparing said present level of battery charge to said calculated total discharge capacity, and   displaying said present level of battery charge as a function of said total discharge capacity.   
     
     
       2. The method of claim 1 further including the step of subtracting a predetermined charge value from said integration of said current to compensate for a self discharge effect of said battery.